Back Up with Mountain Lion’s Time Machine

Time Machine is a most excellent backup system that was introduced with OS X Leopard — and it’s only gotten better. It’s a system because it consists of two parts: the Time Machine System Preferences pane and the Time Machine application.

The Time Machine System Preferences pane and menu.

The Time Machine application is ready to restore a file in the Finder.

To use Time Machine to back up your data automatically, the first thing you need is another hard drive that’s the same size as or larger than your startup disk.

It can be a FireWire hard drive, a USB 2 hard drive, a Thunderbolt hard drive, an SSD (if you can afford to use a Solid State Drive for backups), or even another internal hard drive, if your Mac is a Mac Pro like one of mine.

Another option is an Apple Time Capsule, a device that combines an AirPort Extreme wireless base station with a large hard drive so you can automatically back up one or more Macs over a wired or wireless network.

The first time a new disk suitable for use with Time Machine is connected to your Mac, a dialog asks if you want to use that disk to back up with Time Machine. If you say yes, the Time Machine System Preferences pane opens automatically, showing the new disk already chosen as the backup disk.

If that doesn’t happen, or you want to use an already-connected hard drive with Time Machine, open the Time Machine System Preferences pane, and click the big On/Off switch to On. Now click the Select Disk button, and select the hard drive you want to use for your backups.

The only other consideration is this: If you have other hard disks connected to your Mac, you should click the Options button to reveal the Do Not Back Up list, which tells Time Machine which volumes (disks) not to back up. To add a volume to this list, click the little + button; to remove a volume from the list, select the volume and then click the – button.

The Options sheet also has a check box for warning you when old backups are deleted; check it if you want to be warned. And if your Mac is a laptop, a second check box governs whether Time Machine backs up your Mac when it’s on battery power.

For the record, Time Machine stores your backups for the following lengths of time:

Hourly backups for the past 24 hours

Daily backups for the past month

Weekly backups until your backup disk is full

When your backup disk gets full, the oldest backups on it are deleted and replaced by the newest.

When does it run? Glad you asked — it runs approximately once per hour.

If you enable and set up Time Machine, you’ll never forget to back up your stuff, so just do it.

Time Machine backs up your whole hard disk the first time it runs, and then backs up files and folders that have been modified since your last backup. That’s what backup systems do.

But Time Machine does more — it also backs up things like contacts in your Contacts, pictures in your iPhoto Library, and events in your Calendar calendars, not to mention its support of versions and locking. Those features — sweet ones indeed — make Time Machine unlike any other backup system.